ML20027D216

Adequacy of Station Electric Distribution Sys Voltage,Fort St Vrain Nuclear Generating Station.

ML20027D216
Person / Time
Site:	Fort Saint Vrain
Issue date:	08/31/1982
From:	Udy A EG&G, INC.
To:	Prevatte R Office of Nuclear Reactor Regulation
References
CON-FIN-A-6429 EGG-EA-5914, NUDOCS 8211030186
Download: ML20027D216 (12)

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~ g This is an informal report intended for use as a preliminary or working document fi Prepared for the U.S. Nuclear Regulatory Comission Under DOE Contract No. DE-AC07-761D01570 g E S g G idaho FIN No. A6429 8211030186 820831 PDR RES 8211030186 PDR ,

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FOHM EG4G 39n (Rev 03 M INTERIM REPORT ,

Accession No.

Report No. EGG-EA-5914 C:ntract Program or Project

Title:

Selected Operating Reactors Issues Program (III) 4 Subject of this Document:

Adequacy of Station Electric Distribution System Voltages, Fort St. Vrain Nuclear Generating Station Type of Document:

Informal Report Author (s):

A. C. Udy D:te of Document:

July 1982 I tspor.sible NRC Individual and NRC Office or Division:

R. L. Prevatte, Division of Systems Integration

~

This document was prepared primarily for preliminary or internal use. it has not received full review and approval. Since there may be substantive changes, this document should not be considered final.

EG&G Idaho, Inc.

Idaho Falls, Idaho 83415 e

Prepared for the U.S. Nuclear Regulatory Commission Washington, D.C.

Under DOE Contract No. DE-AC07-76tD01570 NRC FIN No. A6429 INTERIM REPORT

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ADEQUACY OF STATION ELECTRIC DISTRIBUTJ0N SYSTEM V0LTAGES-FORT ST. VRAIN NUCLEAR GENERATING STATION July 1982 A. C. Udy Reliability and Statistics Branch Engineering Analysis Division ,

l EG&G Idaho, Inc.

e j TAC No. 46503 Docket No. 50-267 t \ e e

ABSTRACT 4

This EG&G Idaho, Inc., report reviews the capacity and the capability of the onsite distribution system at the Fort St. Vrain station, in con-junction with the offsite power sources, to automatically start and con-tinuously operate all required safety loads.

FOREWORD This report is supplied as part of the " Selected Operating Reactors Issues Program (III)" being conducted for the U.S. Nuclear Regulatory Com-mission, Office of Nuclear Reactor Regulation, Division of Licensing, by EG&G Idaho, Inc., Reliability and Statistics Branch.

The U.S. Nuclear Regulatory Commission funded the work under the authorization, B&R 20 19 10 11.

Selected Operating Reactors Issues Program (III)

FIN No. A6429 ii

CONTENTS

1.0 INTRODUCTION

...................................................... 1 2.0 DESIGN BASIS CRITERIA ............................................. 1 3.0 SYSTEM DESCRIPTION ................................................ 2 4.0 ANALYSIS DESCRIPTION .............................................. 4 4.1 Sy s tem Mod i f i c a t i o n s . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 e 4.2 Analysis Conditions .......................................... 4 4.3 Analysis Results ............................................. 4 4.4 Analysis Verification ........................................ 5 5.0 EVALUATION ........................................................ 5

6.0 CONCLUSION

S ....................................................... 6 7.0, REFERENCES ........................................................ 7 4

FIGURE

1. Fort St. Vrain unit single-line diagram ........................... 3 TABLE

1. Class lE Equipment Voltage Ratings and L Analyzed Worst Case Load Termi nal Vol tages . . . . . . . . . . . . . . . . . . . . . . . . 2 9

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ADEQUACY OF STATION ELECTRIC DISTRIBUTION SYSTEM VOLTAGES FORT ST. VRAIN huCLEAR GENERATING STATION

1.0 INTRODUCTION

An event at the Arkansas Nuclear One station on September 16, 1978, is described in NRC IE Information Notice No. 79-04. As a result of this

! event, station conformance to General Design Criteria (GDC) 17 is being questioned at all nuclear power stations. The NRC, in a letter of a

August)25,1980, " Adequacy of Station Electric Distribution Systems Volt-ages," required the Public Service Company of Colorado (PSC) to confirm, by analysis, the adequacy of the voltage at the Class lE loads. This letter included 13 specific guidelines to be followed in determining if the load terminal voltage is adequate to start and continuously operate the Class lE loads.

PSC responded with a letter of October 24, 1980.2 hey provided additional information in a let 19, 1981, in a telep conversationofMgrch 27,1981,gerdatedMarchandinlettersdatedApril7,1981,gone and July 6, 1981. {

replaced by submittals Theanalysescontainedinthesesubmittalgwere dated May 28, 1982,7 and June 7 1982. These were discussed in telephone conversations in June 19820 .

Based on the information supplied by the licensee, this report addresses the capacity and capability of the onsite distribution system of the Fort St. Vrain station, in conjunction with the offsite power system, to maintain the voltage for the required Class lE equipment within accept-able limits for the worst-case starting and load conditions.

2.0 DESIGN BASIS CRITERIA The positions applied in determining the acceptability of the offsite l voltage conditions in supplying power to the Class lE equipment are derived I from the following:

1. General Design Criterion 17 (GDC 17), " Electrical Power Systems,"

of Appendix A, " General Design Criteria for Nuclear Power Plants,"

of 10 CFR 50.

2. General Design Criterion 5 (GDC 5), " Sharing of Structures, Systems, and Components," of Appendix A, " General Design Criteria for Nuclear Power Plants," of 10 CFR 50.

3. General Design Criterion 13 (GDC 13), " Instrumentation and Con-trol," of Appendix A, " General Design Criteria for Nuclear Power 2 Plants," of 10 CFR 50. ,

4. IEEE Standard 308-1974, " Class lE Power Systems for Nuclear Power Generating Stations."

5. Staff positions as de datedAugust8,1979{ailedinalettersenttothelicensee; P

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, 6. ANSI C84.1-1977, " Voltage Ratings for Electric Power Systems and

[ Equipment (60 Hz)."

l Six review positions have been established from the NRC analysis guide-lines l and the above-listed documents. These positions are stated in Section 5.0.

3.0 SYSTEM DESCRIPTION Figure 1 is a simplified sketch of the unit single-line diagram of the '

Fort St. Vrain electrical distribution system. It shows that the 480V Class lE buses 1, 2 and 3 are supplied power by independent transformers from 4160V buses 1, 2 and 3 respectively. These three buses are intercon-

• nected to a single reserve auxiliary transformer (RAT) which is the pre-ferred source of offsite power. The alternate source of offsite pcwer is via the unit auxiliary transformer, with the unit generator links removed.

120V Class lE buses lA and 18 are normally supplied power by DC bus powered inverters. Should an inverter be out of service, a connection to 120V bus 3 is available as an alternate source.

1 The licensee supplied the equipment operating ranges identified in Table 1.7 TABLE 1. CLASS lE EQUIPMENT VOLTAGE RATINGS AND ANALYZED WORST CASE TERMINAL V0LTAGES (% of nominal voltage)

Maximum Minimum Analyzed Equipment Condition Rated Analyzed Rated Steady State Transient o

460V Motors & Start -- --

85 --

78.8 Battery Operate 110 110.5 90 91.2 --

Chargers 480V Starters Pickup -- --

90 --

79.1 Dropout -- --

55.4 --

79.1 Operate 114.6 106.0 91.7 93.7' --

Other Equipmentb

a. Established by test.9

b. 120V AC instrument buses are normally supplied power by DC powereo inverters. Use of the alternate source is limited to 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> for one bus by tecnnical specification LCO 4.6.1. i s

2

Notes: .

l. Circuit breakers shown aligned.

for offsite power source.

230kV 230kV Switchyard Switchyard Main ww Reserve ww ransfonner mm Transformer m m 46

^I Auxiliary WW Unit Transformer m m Generator

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4160VAC 4160VAC 4160VAC Bus 1 C Bus 2 C Bus 3 ww ww 0 C C 0 Class 1E Class lE Class 1E C 480VAC 480VAC- l 480VAC Bus 1 Bus 2 Bus 3 Battery dd Battery arger y m%

arger Battery Battery i 1A 1B

! 1 Class lE Class 1E

[Cj 125VDC C 125VDC Bus lA Bus 1B Instrument Power , Instrument Power

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Inverter lA Inverter 1B 4

B P YP P P 1

Class lE Class lE l

120VAC 120/208VAC 120VAC 10 30 10 l Bus lA Bus 3 Bus 18 l

Figure 1. Fort St. Vrain unit single line diagram.

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4.0 ANALYSIS DESCRIPTION 41 System Modifications. The licensee had plans, before the NRC letter was issued, to improve their 480V Class lE switchgear. Included in this modification are the installation of new 4160/480V transformers that have larger capacity and the replacement of the existing bus sections with new bus sections, also of larger capacity. The modifications will be accom-plishedwiththethirdrefuelingoutagefortwoofthebusesandthefgurth refueling outage for the other. The analysis supplied by the licensee

• takes the characteristics and the capacities of the replacement distribution equipment into account.

4.2 Analysis Conditions. PSC has determined by past historical data -

thattgemaximumexpectedoffsitegridvoltageis244kVandtheminimumis 226kV The licensee has analyzed each offsite source to the onsite distribu-tion system under extremes of load and offsite voltage conditions to deter-mine the terminal voltages at the Class lE equipment. The worst case Class lE equipment terminal voltages occur under the following conditions:

1. The worst loading condition occurs when all the loads that operate for a unit startup (unit trip loading is essentially the same) are carried by the reserve auxiliary transformer.

2. The worst transient voltage occurs on the Class lE system under the above condition when starting the 4500 hp non-Class lE boiler feedpump 18 on 4160V bus 2.

3. The highest steady state voltage was determined to occur with a unit shutdown load of $6 megawatts being supplied by the reserve auxiliary transformer.

4.3 Analysis Result. Table 1 shows tne projected worst case Class lE equipment terminal voltages.

The analysis shows that with a worst-case combination of maximum system voltage and minimum shutdown loads, the 460V motors and battery chargers could be subject to voltages slightly in excess (s2V higher) of their max -

imum ratings. The licensee has determined that this equipment could function at this level without damage.9 The analysis shows that the minimum transient voltage can result in load terminal voltages that are less than rated. For the DC system, the battery would supply the load during the period of the transient should the s charger not be able to supply power. No damage would occur and the charger would again supply the load within five seconds. All 460V Class lE motors at the Fort St. Vrain station are built with a service factor of 1.15. This t allows them to operate, without damage, during temporary overloads such as this. The licensee has verified by use of load and motor speed-torque curves that the motors will not stall during these worst'-case analyzed 4

r conditions. During this-transient, a Class lE AC powered contactor may not be able to pick up and start additional loads. However, the analysis shows that no running loads will drop out and that the voltage will recover within ,

a few seconds to allow the contractor pickup.

4.4 Analysis Verification. The computer analysis was verified7 by measuring the voltage at the grid, at the 4160V and 480V buses and at the terminals of the 150 hp fire pump motor, the largest Class lE motor on 480V Class lE bus 1. This was done with the unit operating, with the normally

• energized Class lE loads operating. The voltages were measured for 5 condi-tions--before and during the start of the non-Class 1E 4500 hp t, oiler feed pump, before and during the start of the fire pump and with both of.these o pumps operating. Analyses, to determine the same bus and motor voltages under the same lo2d conditions, were completed using the measured grid volt- -

age and the recorded loads. The accuracy of the licensee's analysis is verified by comparing the results of the analysis with the measured voltages.

Comparison of the measured and the analyzed voltages shows that the difference between the two values is less than 1.1% for the bus voltages and less than 0.23% for the motor terminal voltage for a steady state condition; less than 0.92% for the bus voltages and less than 1.48% for the motor ter-minal voltage when starting either load. In all cases, the measured voltage was higher than the analyzed voltage, showing the conservatism of the computer analysis.

5.0 EVALUATION Six review positions have been established from the NRC analysis guide-linesl and the documents listed in Section 2.0 of this report. Each review position is stated below followed by an evaluation of the licensee submittals.

Position 1--With the minimum expected offsite grid voltage and maximum load condition, each offsite source and distribution syst'em connection com-bination must be capable of starting and of. continuously operating all Class 1E equipment within the equipment voltage ratings.

PSC has shown, by analysis, that the Fort St. Vrain station has suffi-cient capability and capacity for starting and continuously' operating the -

Class lE loads within the equipment voltage ratings (Table 1 and. .

Section 4.3).

Position 2--With the maximum expected offsite grid voltage and minimum a load condition, each offsite source and distribution system connection com-bination must be capable of continuously operating the required Class lE equipment without exceeding the equipment voltage ratings.

8 PSC has shown, by analysis, that the voltage ratings of the Class lE equipment could be slightly exceeded. If this occurs, no equipment damage is expected.

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3 Position 3--Loss of offsite power to either of the redundant Class lE distribution systems, due to operation of voltage protection relays, must not occur when the offsite power source is within expected voltage limits.

EG&G Idaho, Inc., will verify, in a separate report, that the require-ments of this position are satisfied (TAC No. 46504).

Position 4--The NRC letterI requires that test results verify the accuracy of the voltage analyses supplied.

4 PSC has verified the accuracy of the voltage analysis.

Position 5--No event or condition should result in the simultaneous or a consequential loss of both required circuits from the offsite power network to the onsite distribution system (GDC 17).

The licensee has analyzed the Fort St. Vrain connections to the offsite power grid, and has determined that no potential exists for either the sim-ultaneous or the consequential loss of both circuits from the offsite grid.

Position 6--As required by GDC 5, each offsite source shared between .

units in a multi-unit staticn must be capable of supplying adequate starting and operating voltage for all required Class lE loads with an accident in one unit and an orderly shutdown and cooldown in the remaining units.

This applies to multi-unit stations. It does not apply to the single-unit Fort St. Vrain station.

6.0 CONCLUSION

S The voltage analyses submitted by PSC for the Fort St. Vrain station were evaluated in Section 5.0 of this report. It was found that:

1. Voltages within the operating limits of the C. lass lE equipment are supplied for all projected combinations of plant load and offsite power grid conditions.

2. The licensee has performed a test that verifies the accuracy of the analysis.

3. PSC has determined that no potential exists for either a-simulta-neous or a consequential loss of both offsite power sources.

EG&G Idaho, Inc., is performing a separate review of the undervoltage relay protection at the Fort St. Vrain station. This will evaluate the g relay setpoints and time delays to determine that spurious tripping of the '

Class lE buses will not occur with normal offsite source voltages.

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7.0 REFERENCES

1. NRC letter, R. L. Tedesco, to P.S.C. (Warenbourg), " Adequacy of Station Electric Distribution Systems Voltage," August 25, 1980.

2. PSC letter, F. E. Swart to R. L. Tedesco, NRC, " Emergency Power Systems," October 24, 1980, P-80373.

3. PSC letter, F. E. Swart to A. Udy, EG&G Idaho, Inc. (EG&G), " Response a to your Request for Additional Information on the Adequacy of Station Electric Distribution System Voltages," March 19, 1981, ND-81-0076.

e 4. Telecon, A. Udy, EG&G Idaho and J. Reesy, PSC, March 27, 1981.

5. PSC letter, F. E. Swart to A. Udy, EG&G Idaho, " Response to your Request for Additional Information on the Adequacy of Station Electric Distribution System Voltages," April 7, 1981, ND-81-0089.

6. PSC letter, H. L. Brey to A. Udy, EG&G Idaho, " Load Flow Analysis of Fort St. Vrain 4160V and 480V Buses," July 6, 1981, ND-81-0164.

7. PSC letter, H. L. Brey to G. Kuzmycz, NRC, " Electrical Power Systems,"

May 28,1982.

8. PSC letter, H. L. Brey to G. Kuzmycz, NRC, " Electrical Power Systems,"

June 7, 1982.

9. Telecon, A. Udy, EG&G Idaho, and M. Niehoff, PSC, June 14 and 16, 1982.

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